Your friend has been given a laser for her birthday. Unfortunately, she did not

Question

Your friend has been given a laser for her birthday. Unfortunately, she did not receive a manual with it and so she doesn't know the wavelength that it emits. You help her by performing a double-slit experiment, with slits separated by 0.18 mm. You find that the distance between the first bright fringe above the central maximum and the first bright fringe below the central maximum is delta y = 5.3 mm (Figure 1) The screen is 1.4 m away from the slits. What is the value of m in the equation d sin theta = m lambda for the first bright fringe below the central maximum? Express your answer using one significant figure. m = -1 What is the wavelength the laser emits? Express your answer to three significant figures and include the appropriate unit.

Explanation / Answer

here,

screen distance, D = 1.4 m

displacementon screen, Y = 5.3 mm = 5.3*10^-3 m

slit seperation, d = 0.18*10^-3 m

From diffraction experiment

Y = m * wavelength * D/d

wavelength = Y/D * d/m

wavelength = (5.3*10^-3)/1.4 * (0.18*10^-3) / 1

wavelength = 6.814*10^-7 m or 681.4 nm

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